Starter drive

ABSTRACT

A starter drive for combustion engines has a motor on whose rotatable output shaft is mounted a pinion having freedom of rotation as well as axial displacement relative to the shaft. A motion-transmitting arrangement is provided, including a funnelshaped motion-transmitting element rotatable with the shaft surrounding the same and located adjacent one end of the pinion with its open side facing the latter, and an elastically yieldable annular coupling member surrounding and fast with the pinion at the one end thereof and conically converging on its outer periphery towards the funnel-shaped element so that, when the coupling member is received in the latter, frictional motiontransmission will be established between the shaft and the pinion.

United States Ptent Ruhle et al. Q

[451 May 30, 1972 [54] STARTER DRIVE [72] inventors: Walter Ruhle,Korntal; Otto Barthruff,

Stuttgart, both of Germany [73] Assignee: Robert Bosch Gmbll, Stuttgart,Germany [22] Filed: Oct. 21, 1970 [211 App]. No.: 82,608

[51] Int. Cl ..F02n 15/08 [58] Field ofSearch ..290/38, 38 A, 48

[ 56] References Cited UNITED STATES PATENTS 2,455,328 11/1948 Buxton..290/38 2/1954 Uher ..290/48 Primary ExaminerBemard A. GiiheanyAssistant Examiner-W. E. Duncanson, Jr. Attorney-Michael S. StrikerABSTRACT A starter drive for combustion engines has a motor on whoserotatable output shaft is mounted a pinion having freedom of rotation aswell as axial displacement relative to the shaft. A motion-transmittingarrangement is provided, including a funnel-shaped motion-transmittingelement rotatable with the shaft surrounding the same and locatedadjacent one end of the pinion with its open side facing the latter, andan elasticaily yieldable annular coupling member surrounding and fastwith the pinion at the one end thereof and conicaily converging on itsouter periphery towards the funnel-shaped element so that, when thecoupling member is received in the latter, frictionalmotion-transmission will be established between the shaft and thepinion.

9 Claims, 1 Drawing Figure Patented May 30, 1972 INVENTOR Unrez R m a I01-7-0 BMTH ATTORNEY STARTER DRIVE I BACKGROUND OF THE INVENTION Thepresent invention relates generally to starter drives, and moreparticularly to starter drives for combustion engines.

Among the various types of starter drives for combustion engines whichare known in the art, one known type utilizes an electromotor having arotatable output shaft on which there is mounted a sleeve shiftablelengthwise of the shaft and surrounded by the drive pinion which inknown manner can be brought into mesh with gears for driving thecombustion engine which is to be started. The pinion and the sleevesmesh threadedly, and a friction coupling utilizing a rubber ring isprovided for transmitting torque to the pinion. In this prior-artconstruction the rubber ring is compressed axially-when torque is to betransmitted-between one flange which is fast with the output shaft andanother flange which is fast with the sleeve. The rubber ring completelyfills the space in which it is located after the sleeve has travelledonly a short distance to effects its compression, so that thefriction-coupling in effect becomes rigid when this takes place. Thishas been found to be disadvantageous, however, especially at the momentwhen the gear teeth of the pinion first contact the teeth of the gearwhich they are to drive, that is the gear which in turn is coupled insuitable manner with the combustion engine to be started.

A further known construction utilizes a similar coupling ring which,however, is radially expanded by wedge-shaped members or angular leverslocated within the confines of the ring, when torque is to betransmitted. This guarantees a gentle meshing of the teeth of the pinionwith those of the gear to which motion is to be transmitted, even if therespective teeth first contact one another in end-to-end relationship.However, although-this construction overcomes the disadvantage of theone described previously, this second construction requires a relativelycomplicated and expensive arrangement for effecting the radial expansionof the ring, and this results not only in correspondingly larger spacerequirements for the finished drive, but also substantially increasesthe expense involved in producing and selling the same.

It follows, therefore, that what is missing in this field is a starterdrive of the type under discussion which affords the advantages but doesnot possess the disadvantages of the known prior-art constructions.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide a starter drive of the type under discussion whichavoids the aforementioned disadvantages and provides the advantagesindicated above as desirable.

More particularly it is an object of the present invention to providesuch a starter drive which guarantees under all operat ing conditions agentle meshing of the teeth of its pinion with those of a gear to whichthe pinion is to transmit motion.

A concomitant object of the invention is to provide such a starter drivewhich is simple and comparatively inexpensive in its construction, andtherefore will have a correspondingly low selling price.

An additional object of the invention is to provide such a starter drivewhich is compact and has small space requirements, and which because ofits simplicity is highly reliable and not prone to malfunctioning.

In pursuance of the above objects, and others which will become apparenthereafter, one feature of the invention resides in a starter drive forcombustion engines which, according to one embodiment, and brieflystated, comprises a a motor having a rotatable output shaft and a pinionon the shaft axially and rotationally displaceable relative thereto.Motiontransmitting means is provided and includes a funnel-shapedmotion-transmitting element rotatable with the shaft and surrounding thesame adjacent one endof the pinion and having an open side facing thelatter, and an elastically yieldable annular coupling member tightlysurrounding said one end and conically converging towards themotion-transmitting element so as to be receivable in the latter infrictionally motion-transmitting relationship.

The funnel-shaped motion-transmitting element is threaded onto theshaft, for which purpose it and a cooperating portion of the shaft areprovided with meshing steep-pitched threads. The pinion has a hubprovided at the aforementioned end with a cylindrical extension on whichthe annular coupling member is located surrounding the extension. Byconfigurating the annular coupling member of conical or frustoconicalshape, and by making the motion-transmitting element of a similarconfiguration, namely essentially funnel-shaped, it is possible toobtain a continuous increase of the pressure with which themotion-transmitting element engages the coupling member, depending uponthe magnitude of the torque to be transmitted, without the elasticproperty of the coupling member being destroyed. In other words thedifficulty of the earliermentioned prior-art constructions, wheredespite the fact that the coupling member is a rubber ring thearrangement once engaged becomes rigid to all intents and purposes, isavoided with the present construction because the elastic properties ofthe coupling member are retained under all operating conditions. it willbe appreciated, of course, that the motion-transmitting element willmove axially of the shaft when the motor is energized, under theinfluence of inertial forces, threading itself along the shaft andengaging the coupling member and pressing against the same forfrictional motion-transmitting engagement.

A further advantage of the construction according to the presentinvention resides in the fact that in arrangements where there is asignificant difierence between the RPM of the output shaft under no-loadconditions and the starting RPM of the combustion engine, the presentstarter drive will act as a slip coupling between the engaged pinion andthe starter motor when the combustion engine has caught and is runningunder its own power; below the no-load RPM of the starter motor orbefore deenergization of the starter motor, the drive according to thepresent invention prevents a disengagement of the pinion from thecooperating gear of the combustion engine so that a reliable tuming-overof the combustion engine will always be assured. I g

The novel features which are considered as characteristic for theinvention are setforth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation together with additional objects and advantages thereof willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE illustrates inpartially sectioned, partially broken-away fragmentary view anembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing indetail it will be seen that reference numeral 11 identifies a startermotor, generally an electrically operated motor, having a rotatableoutput shaft 10. Such motors are well known and any of the various typesconventionally used in starter drives may be employed. The output shaft10 has a first section 10a with an outer circumferential surface whichis smooth, and a second section 10b which is provided with asteep-pitched external thread 12. A pinion 13 is mounted on the section10a, having freedom of rotation with reference to the shaft 10 as wellas freedom of axial displacement relative to the shaft 10, or rather tothe section 10a. The pinion 13 has a cylindrical hub 13a and an annulus13b of gear teeth which is to be brought into meshing engagement withthe annulus of gear teeth provided on a gear 14 when the starter driveis to operate for starting a combustion engine. The gear 14 has beenshown only fragmentarily, it being evident from the context of the priorart that such a gear will have an outer annulus of gear teeth, and itbeing further evident that such a gear will be connected in suitable andentirely conventional manner with a non-illustrated combustion enginewhich is to be turned over as the gear 14 is rotated by the pinion 13.

According to the present invention an annular coupling member 15 ofelastically yieldable material, for instance a synthetic plasticmaterial, is mounted on the cylindrical hub 13a of pinion 13; one axialend face of the annular element 15 is supported by the adjacent endfaces of the gear teeth of the annulus 13b on the pinion 13. As thedrawing clearly shows, the outer circumferential surface of the couplingmember 15 converges frusto-conically in direction away from the pinion13.

The end face of the member 15 which faces the gear teeth of the annulus13b may abut directly against the latter, but it is preferable-4n orderto protect the material of the member 15 against damage-to insert awasher 16 between the member 15 and the annulus 13b, such a washersurrounding the hub 13a as illustrated and advantageously having smoothmajor surfaces.

Whereas the member 15 constitutes a part of the novelmotion-transmitting means in the novel starter drive illustrated by wayof the exemplary embodiment, a funnel-shaped motiontransmitting element17 constitutes a cooperating part of the motion-transmitting means. Itwill be seen that the element 17 surrounds the section b of the outputshaft 10, and it is to be understood that the inner surface of its hubwhich surrounds and engages the section 10b is provided withscrewthreads which mate with the steep-pitched screwthread 12 on thesection 101;. The hub itself is identified with reference numeral 17aand the drawing clearly shows that the conically diverging open side ofthe element 17 faces towards the pinion l3 and therefore towards thecoupling member 15. Because of the cooperating screwthreads on thesection 10b and the hub 17a of the element 17, the latter can undergodisplacement longitudinally of the shaft section 10!; by turningrelative to the latter.

A helical expansion spring 18 is provided at that axial end of thepinion 13 which is remote from the element 17; as illustrated, thespring 18 surrounds a portion of the section 10a and bears with one endagainst the pinion 13 and with the other end against an abutment 19which is fastened in suitable manner on the section 10a of the shaft 10.The spring 18 therefore tends to continuously urge the pinion 13 towardsthe right-hand side in the FIGURE, that is it tends to maintain thepinion 13 out of mesh with the teeth of the gear 14. At the same time,it tends to press the outer circumferential surface of the couplingmember into contact with the corresponding conically tapered innercircumferential surface 17b of the element 17. A shoulder 10c providedon the shaft 10 and'constitutes a terminal abutment for the element 17when the pinion 13 is in its rest or inoperative position illustrated inthe FIGURE.

It is pointed out that the member 15 may be produced as a discretemember and may be secured in suitable manner, as by cooperatingprojections, by bonding or in any other feasible way, on the hub 13a soas to be rotatable with but not relative to the same. The pinion itselfmay be of metal, or of other suitable materials. The member 15 may be ofrubber or a synthetic plastic. In certain circumstances, for instance ifthe starter drive is of low-capacity type, for instance if it isrequired to supply less than 0.2 hp, the pinion 13 and the member 15 maybe made for instance by injection molding of synthetic plastic material,and may be of one piece.

The operation of the novel starter drive as illustrated by way ofexample in the drawing, will be evident from what has been set forth.When the motor 11 is energized with corresponding rotation of the outputshaft 10, the inertia of the element 17 causes the same to twistforwardly (towards the left-hand side in the drawing) on the steep-pitchthread 12 and to thereby push the pinion 13 in the same directionagainst the urging of the spring 18 until the teeth 13b mesh with theteeth of the gear 14. 1f the teeth of the pinion 13 enter into thespaces between the teeth of the gear 14, then the pinion 13 continues tobe displaced forwardly until it abuts against the abutment ring 19.Continued rotation of the shaft 10 causes the element 17 to press moretimily against the member 15, because the pinion 13 has now becomestationary with respect to the axial direction of the shaft 10 while thesteeplypitched thread 12 continues to permit the element 17 to advanceaxially towards the pinion 13. This continues until the frictionalforces developing as a result between the element 17 and the member 15,and between the member 15 and the pinion 13. have reached a valuesufficient to transmit the torque of the shaft 10 via the thread 12, themember 15 and the pinion 13 into the gear 14 of the combustion engine,which thus turns over.

If, on the other hand, the teeth of the pinion do not move into thespaces between the teeth of the gear 14 initially, but instead if theteeth of the pinion l3 first contact and abut against the teeth of thegear 14 in end-to-end relationship, with the meshing engagement of thepinion 13 with the gear 14 being initially prevented, the pressurebetween element 17 and member 15, and between member 15 and pinion 13continues to increase until it suffices to turn the pinion 13 withreference to the gear 14 until the teeth of the pinion 13 become alignedwith the spaces between the teeth of the gear 14 whereby the pinion 13is enabled to continue its forward movement into meshing engagement withthe gear 14 as before.

When the pinion 13 meshes with the teeth of the gear 14, torque istransmitted through frictional engagement between the element 17 and themember 15, and between the member 15 and the pinion 13. It follows fromthis that it is actually possible for the member 15 only to tightlysurround and engage the hub 13a of the pinion, and not to benon-rotatably connected thereto although this is an additionalpossibility. in any case, a continuous accommodation of the pressurewith which the element 17 engages the member 15 is obtained, dependingupon the magnitude of the torque which is to be transmitted. At the sametime it is assured, during start-up of the combustion engine which forthe time being is coupled with the motor 11, that the pinion 13 will notmove out of mesh with the gear 14 until the combustion engine turns overunder its own power.

This, however, requires a certain differential between the RPM of themotor 11 under no-load conditions and the RPM at which the combustionengine will rotate under its own power. If, for instance, the combustionengine will turn over momentarily under its own power, load is removedfrom the motor 11. The engaging pressure between the element 17 and themember 15 drops to a low level so that the element 17 and the member 15can rotate with reference to one another with the drive acting as a slipcoupling. Because of the removal of the load acting upon it, the motor11 will increase its RPM and consequently restore pressure of theelement 17 on the member 15. If, now, the combustion engine does notcontinue to turn over under its own power, that is if it has done soonly briefly as mentioned before but has stopped again, then thetransmission of torque in a sense starting the combustion enginecontinues.

On the other hand, once the combustion engine has started and is runningunder its own power with its RPM increasing, the starter drive againacts as a slip coupling with the pinion 13 remaining in mesh with theteeth of the gear 14 until such time as the gear 14 reaches a number ofrevolutions per minute corresponding to the RPM of the motor 11 underno-load conditions, or until such time as the motor 1 1 is de-energized.When the RPM of the combustion engine and therefore of the gear 14exceeds the RPM of the output shaft 10 of the motor 11, and only at suchtime, the element 17 again begins to perform a twisting movement withreference to the shaft section 10b due to the influence of the gear 12,but this time in reverse direction, namely towards the right-hand sidein the FIGURE. This permits the spring 18 to displace the pinion towardsthe right whereby meshing engagement of the pinion 13 with the gear 14is terminated.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in astarter drive for combustion engines, it is not intended to be limitedto the details shown, since various modifications and structural changescan be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended 1. A starter drive for combustion engines,comprising an electromotor having a rotatable output shaft; a pinionmounted on said shaft for axial displacement relative thereto from anormal rest position to an operating position, said pinion having at oneaxial end a portion of reduced diameter; an annular coupling ring ofelastically yieldable material mounted on said portion of reduceddiameter, and having an outer circumferential surface which conicallytapers axially of said pinion in direction from the operating positionof said pinion to the rest position thereof; a discrete funnel-shapedmotion-transmitting member surrounding said shaft adjacent said oneaxial end of said pinion and movable relative thereto, and having adivergent open side facing saidcoupling ring; cooperating steep-pitchthreads on said member and said shaft for enabling the former to advancealong the latter under the influence of inertial force in response torotation of said shaft, to thereby contact and initially axiallydisplace said pinion to said operating position with subsequentfrictional transmission of motion from said member via said ring to saidpinion; and biasing means surrounding said shaft adjacent the otheraxial end of said pinion and permanently urging said pinion axially ofsaid shaft and into said open side of said motion-transmitting member.

2. A starter drive as defined in claim 1, said pinion having aperipheral annulus of gear teeth, and said coupling ring having an axialend face directed towards said other end and supported by said gearteeth.

3. A starter drive as defined in claim 2; further comprising a washersurrounding said extension intermediate said gear teeth and couplingring for protecting the latter against damage from the former.

4. A starter drive as defined in claim 1, said coupling ring beingunitary with said pinion.

5. A starter drive as defined in claim 1, wherein at least one of saidcoupling ring and pinion consists of synthetic plastic material.

6. A starter drive as defined in claim 1, wherein said coupling ring andsaid pinion both consist of synthetic plastic material.

7. A starter drive as defined in claim 1, wherein said coupling ringconsists of, and said pinion at least predominantly consists ofsynthetic plastic material.

8. A starter drive as defined in claim 1, said biasing means comprisinga helical spring surrounding said shaft adjacent said other end of saidpinion and bearing upon the latter and an abutment, respectively.

9. A starter drive for combustion engines, comprising a motor having arotatable output shaft; a pinion on said shaft axially and rotationallydisplaceable relative thereto; and motion-transmitting means, includinga funnel-shaped motiontransmitting element rotatable with said shaftsurrounding the same agg'acent one end of said pinion and having an openside facing e latter and an elastically yieldable annular couplingmember surrounding and engaging said one end and conically convergingtowards said element so as to be receivable in the latter infrictionally motion-transmitting relationship.

1. A starter drive for combustion engines, comprising an electromotor having a rotatable output shaft; a pinion mounted on said shaft for axial displacement relative thereto from a normal rest position to an operating position, said pinion having at one axial end a portion of reduced diameter; an annular coupling ring of elastically yieldable material mounted on said portion of reduced diameter, and having an outer circumferential surface which conically tapers axially of said pinion in direction from the operating position of said pinion to the rest position thereof; a discrete funnel-shaped motion-transmitting member surrounding said shaft adjacent said one axial end of said pinion and movable relative thereto, and having a divergent open side facing said coupling ring; cooperating steep-pitch threads on said member and said shaft for enabling the former to advance along the latter under the influence of inertial force in response to rotation of said shaft, to thereby contact and iniTially axially displace said pinion to said operating position with subsequent frictional transmission of motion from said member via said ring to said pinion; and biasing means surrounding said shaft adjacent the other axial end of said pinion and permanently urging said pinion axially of said shaft and into said open side of said motion-transmitting member.
 2. A starter drive as defined in claim 1, said pinion having a peripheral annulus of gear teeth, and said coupling ring having an axial end face directed towards said other end and supported by said gear teeth.
 3. A starter drive as defined in claim 2; further comprising a washer surrounding said extension intermediate said gear teeth and coupling ring for protecting the latter against damage from the former.
 4. A starter drive as defined in claim 1, said coupling ring being unitary with said pinion.
 5. A starter drive as defined in claim 1, wherein at least one of said coupling ring and pinion consists of synthetic plastic material.
 6. A starter drive as defined in claim 1, wherein said coupling ring and said pinion both consist of synthetic plastic material.
 7. A starter drive as defined in claim 1, wherein said coupling ring consists of, and said pinion at least predominantly consists of synthetic plastic material.
 8. A starter drive as defined in claim 1, said biasing means comprising a helical spring surrounding said shaft adjacent said other end of said pinion and bearing upon the latter and an abutment, respectively.
 9. A starter drive for combustion engines, comprising a motor having a rotatable output shaft; a pinion on said shaft axially and rotationally displaceable relative thereto; and motion-transmitting means, including a funnel-shaped motion-transmitting element rotatable with said shaft surrounding the same adjacent one end of said pinion and having an open side facing the latter and an elastically yieldable annular coupling member surrounding and engaging said one end and conically converging towards said element so as to be receivable in the latter in frictionally motion-transmitting relationship. 